“While performances have occasionally been called off on past election nights, many more have been canceled this year, as producers bet that it will be tough for music and drama to compete with history. That is partly a reflection of the high interest in the race pitting Donald J. Trump against Hillary Clinton, which has already broken television ratings records at several points. And it is partly a bow to the ascendancy of the smartphone, which has left audiences more connected — and more distractible — than ever.”